some info on Chevy Quadrajet intake flow

[Mudsport96]

So, I myself have asked the question, "How well do the factory intakes flow?" And Cliff himself has done testing of aftermarket against factory Pontiac intakes and had great results.

But, if you look at Poncho intakes vs Chevy small block intakes, the Pontiacs look more performance oriented than the chevy counterparts. For example, the Chevy has a literal "T" in the rear runners that can't be good for velocity. After some looking around i found as cast factory intake and ported factory intake numbers for a page out of David Vizards performance Chevy book. I also found as cast and ported flow numbers for an Edelbrock Performer RPM.




As you can see, a ported factory manifold is on par with an RPM

[Cliff Ruggles]

Good info.

One also has to realize with this topic that peak flow numbers don't tell the story about how well any particular intake is going to work in actual use.

The stock Chevy spread bore intakes are excellent, always have been.  They were very well designed with sufficient runner volume to keep port velocity high and produce a very broad power curve.  They work very well in the "normal" rpm range, and will easily support a very well though out small block engine build past 400hp and 5500rpms.

They really don't take a back seat to any of the aftermarket offerings until way up near the shift point for most street and street/strip engine builds.

Although a little time consuming and labor intensive, they can be modified under the carburetor to the same apprx size/shape as a Performer or Performer RPM intake which really wakes them up, and it does it without making the runners larger and slowing down the air velocity to the cylinder head intake ports.

The factory Pontiac intakes are very similar to the SBC units, have very wide plenum areas and well designed runners with adequate runner volume to support pretty big HP. 

My factory iron intake is from a 1971 400 engine.  It is modified under the carb as mentioned above, but only port matched, no porting in the runners anyplace.  On the dyno we back to back tested it against the much larger and highly praised Edelbrock RPM intake.  The RPM intake was also gasket matched to the heads being used. 

The test engine was a 428cid engine with aftermarket aluminum heads with 260cfm intake runners, custom ground hydraulic roller cam with 236/242 @ .050" specs and .577" lift.

The "modified" factory intake made 497hp, the RPM made 491hp, no other changes!

Think about that testing for just a moment, and you will see that the larger intake brought NOTHING to the table even though it still had larger runners, smoother turns with those runners, and over 1" taller!  The RPM intake was also DOWN on average power as well, which is what we look more closely at that peak power, as a typical street engine must operate over a broad rpm range and it typically pushing around a relatively heavy vehicle with moderate gearing/converter.

Another thing to consider is that an RPM intake is considerably taller making it difficult, if not near impossible to use with factory Ram Air, Shaker hoods, etc.  It also requires some "cobbling" to use as the throttle cable quickly becomes too short, factory fuel lines woln't reach the carb, and you loose your divorced choke for early factory carbs, and the later Hot Air chokes must be converted to electric.

Folks don't often consider any of this when purchasing aftermarket "high performance" parts that they believe are going to give them better performance, when in many cases the only real performance benefit is the weight savings over the factory iron intake.

I'm not trying to down-play aftermarket parts here, but I love going "against the grain" with these things.  Going to our local 1/8th mile track on a Friday night test and tune session and running low 7's over 96mph in full street trim with a factory intake, q-jet, HEI, stock valve covers, on 8" wide DOT's thru quiet exhaust....well.....then looks you get in the staging lanes are PRICELESS!.......Cliff

[qjetsrule]

another note to how well these intakes were engineered and tested is that they also had to pass emissions. the aftermarket had a free ride to develop any way they wanted yet as Cliff testifies, they still could not beat the factory engineers. it's too bad so many well designed factory manifolds were tossed.

[Mudsport96]

The looks are priceless Cliff you are right. I have only had the car at the track once, and that was before the traction bars. I had also left the slicks at home because in the rush they were forgotten. So after the first pass flopped because the secondary lockout tang had come loose and only let me make a run on the primaries (God that was embarrassing). The guy next to my trailer in the pit said "it'll run better with a Holley, those quadrajets are junk." I got that taken care of, and the old 1980s Montgomery Ward 195/70r14 radials never had a chance. People thought I blew the car up by the sixty foot mark because there was so much smoke from the dry old tires. I'll have to find the slip, its something rediculous like 19.5 @98mph.
When I got back to the trailer I was putting the car up because the was no point in making a pass on those tires. The guy next to me asked what I had done to the carb to make it run like that. And I answered "made the secondaries open"

[AHotRod]

So, I myself have asked the question, "How well do the factory intakes flow?" And Cliff himself has done testing of aftermarket against factory Pontiac intakes and had great results.

But, if you look at Poncho intakes vs Chevy small block intakes, the Pontiacs look more performance oriented than the chevy counterparts. For example, the Chevy has a literal "T" in the rear runners that can't be good for velocity. After some looking around i found as cast factory intake and ported factory intake numbers for a page out of David Vizards performance Chevy book. I also found as cast and ported flow numbers for an Edelbrock Performer RPM.




As you can see, a ported factory manifold is on par with an RPM

Could you repost the pictures of the flow numbers?

Or do you have it in a PDF file?

Thank You,
Glenn

[Mudsport96]

I'll have to see, both my computer and old phone died since then. Give me some time to look

[Mudsport96]

Ok the blue and red picture is a stock flow and ported flow factory intake. And the other explains itself.